Question

Difficulty: HardKingdom Fungi: Moulds, Yeasts, and Mushrooms

Place the following events in the sexual reproduction life cycle of a mushroom (*Agaricus*) in the correct chronological sequence from initial hyphal interaction to spore germination.

  1. 1Hyphal fusion (plasmogamy) between compatible monokaryotic mycelia to form a dikaryotic mycelium
  2. 2Growth and differentiation of the dikaryotic basidiocarp (fruiting body)
  3. 3Nuclear fusion (karyogamy) within basidia located on the gill surfaces
  4. 4Meiotic division of the diploid nucleus producing four haploid basidiospores
  5. 5Discharge of basidiospores and subsequent germination into new primary monokaryotic mycelia

Answer

The correct chronological sequence of events in the sexual reproduction of *Agaricus* is: (1) Hyphal fusion (plasmogamy) between compatible monokaryotic mycelia to form a dikaryotic mycelium, (2) Growth and differentiation of the dikaryotic basidiocarp (fruiting body), (3) Nuclear fusion (karyogamy) within basidia located on the gill surfaces, (4) Meiotic division of the diploid nucleus producing four haploid basidiospores, and (5) Discharge of basidiospores and subsequent germination into new primary monokaryotic mycelia.
In the life cycle of the mushroom (*Agaricus*), sexual reproduction begins when two compatible monokaryotic hyphae undergo plasmogamy (cytoplasmic fusion) to yield a dikaryotic mycelium. This dikaryotic mycelium grows and develops into the macroscopic basidiocarp (mushroom). Within the microscopic basidia on the gills, karyogamy (nuclear fusion) occurs, creating a diploid nucleus. This nucleus undergoes meiosis to form four haploid basidiospores, which are eventually shed and germinate into new monokaryotic primary mycelia.

Step-by-Step Solution

1
Identify the initial cellular fusion phase
Plasmogamy fuses cytoplasm of two compatible haploid monokaryotic hyphae without immediate nuclear fusion.
Sexual reproduction initiates when two compatible mating strains meet in the soil substrate.
2
Trace vegetative growth to reproductive structure development
The dikaryotic mycelium expands and produces the visible basidiocarp (mushroom).
The mushroom fruiting body consists entirely of dikaryotic hyphal tissues.
3
Locate the site of true nuclear fusion
Karyogamy occurs within specialized cells called basidia on the gill surfaces.
Nuclear fusion is delayed until the fruiting body forms mature gills.
4
Determine the reductive division event
Meiosis reduces the diploid zygotic nucleus into four haploid nuclei, forming basidiospores.
Meiosis restores the haploid genome before spore dispersal.
5
Complete the cycle with dispersal and growth
Basidiospores drop from gills, disperse by wind, and germinate into monokaryotic mycelia.
Spore germination completes the cycle by producing new primary haploid mycelia.

Key Concept

Life cycle of Basidiomycetes: Plasmogamy, Dikaryotic basidiocarp growth, Karyogamy, Meiosis, and Spore germination
Estimated Time:2m 0s
Rate this question